Conventional PVD chambers include a target of the material to be sputtered, which target is connected to a source of power, a gas inlet for an inert gas such as argon and other gases, such as nitrogen, if required, and a substrate support mounted parallel and spaced from the target, which is biased. During sputtering, argon atoms become energized and strike the target, sputtering off atoms of the target material which then deposit on the substrate. In order to enhance the sputtering rate, a magnet pair is mounted above the target on the outside of the chamber. The magnet pair increases the momentum at which argon atoms strike the target.
FIG. 1 is a schematic cross sectional view of a typical sputtering chamber. A vacuum chamber 10 includes a target 12 of the material to be sputtered, and a substrate support 14. A source of DC power 13 is connected to the target 12. A pair of opposed magnets 16, 18 are mounted above the target 12. A power source 20, such as a source of RF power, is connected to the substrate support 14. During sputter deposition, a substrate 22 is mounted on the substrate support 14. A gas inlet 19 permits gases to be passed into the chamber. Argon is generally used as the sputtering gas. It is ionized in the chamber and is attracted to the target 12 by the negative potential of the target 12. The argon ious strike the surface of the target and sputter off particles of target material which deposit on the substrate 22.
As the features of semiconductor devices continue to become smaller, it is more difficult to fill the bottoms of small diameter, high aspect ratio openings by sputtering. Sputtering takes place in random directions and thus most of the sputtered material is deposited on land portions rather than in openings in the substrate. Further, since the sputtered particles enter openings in non-vertical directions, they impact the sidewalls and thus only a small proportion of the sputtered particles deposit on the bottom of the openings. This is shown in FIG. 2, wherein an opening 100 is partially filled with sputtered material 110.
In an attempt to improve the directionality of the sputtered particles, collimators have been tried, but they have been unable to greatly improve filling of small diameter, high aspect ratio openings.
Thus an improved sputtering chamber has been designed that includes an internal helical coil connected to a source of RF power. FIG. 3 is a schematic cross sectional view of this improved sputtering chamber, designated as an "ionized metal plasma" or "IMP" chamber. The IMP chamber 170 includes a conventional target 172 mounted on a top wall 173 of the chamber 170. A pair of opposing magnets 176, 178, are mounted over the top of the chamber 173. A substrate support 174 bearing a substrate 175 thereon, is mounted parallel to and spaced from the target 172. A source of power 180 is connected to the target 172 and a source of RF power 182 is connected to the substrate support 174. A controller 200 regulates gas flows. A helical coil 185 is mounted inside the chamber 170 between the target 172 and the substrate support 174, and is connected to a source of RF power 188. Gases in vessels 192, 194 are metered to the chamber by means of flow valves 196, 198.
The pressure in the chamber is maintained by a cryogenic pump 190 through an inlet 191 via a three position gate valve 199. Providing that the pressure in the chamber is fairly high, i.e., about 30-40 millitorr, the internal inductively coupled coil 186 provides a high density plasma in the region between the sputtering cathode or target 172 and the substrate support 174. Thus sputtered target atoms become ionized and positively charged as they pass through the high density plasma region. They are attracted by the negatively biased substrate and thus impact the substrate in a more vertical direction than occurs in conventional PVD chambers.
Conventional PVD chambers as shown in FIG. 1 are generally operated at low pressures of about 1-5 millitorr. Under the higher pressures in the IMP chamber, re-sputtering of target material onto the target occurs more frequently. Material that is sputtered from the target in an IMP chamber at higher pressures has a higher possibility to collide with argon molecules, changing the original direction of the sputtered particles. If such a collision occurs close to the target surface, it can be re-directed back towards the target where it re-deposits. Thus the problems of erosion and re-deposition are more severe in the IMP chamber than in conventional PVD chambers. These re-deposited particles are less adherent to the target, and they can flake off as particles, which is always undesirable.
Since it is known that the shape of the magnets for the target have an impact on the uniformity of erosion of the target during sputtering, improved magnet shapes were investigated.